for (i in unique(raw_area_long$date)){sub.dat<-subset(raw_area_long, raw_area_long$date==i) umoles<-(((sub.dat$area[sub.dat$date==i]-calib_coeff$intercept[calib_coeff$date==i])/calib_coeff$slope[calib_coeff$date==i])/1000)*sub.dat$headspace_mL[sub.dat$date==i]}
for (i in unique(raw_area_long$date)) { sub.dat <- subset (raw_area_long, raw_area_long$date == i) umoles <- ( ( ( sub.dat$area[sub.dat$date == i] - calib_coeff$intercept [calib_coeff$date == i] ) / calib_coeff$slope [ calib_coeff$date == i] ) / 1000 ) * sub.dat$headspace_mL }